Viscosity change compensation for hydraulic feed systems



March 23, 1954 c. DEVAUD 2,672,730 VISCOSITY CHANGE COMPENSATION FOR-HYDRAULIC FEED SYSTEMS Filed May 28, 1951 3 Sheets-Sheet l 6 Fig.2

March 23, 1954 VISCOSITY CHANGE COMPENSATION FOR Filed May 28, 1951INA/\A/W 20 I t: 45 H Jk i: )k i A E k l i 45 h E /n/x m z/ March 23,1954 DEVAUD 2,672,730

VISCOSITY CHANGE COMPENSATION FOR HYDRAULIC FEED SYSTEMS Filed May 28,1951 3 Sheets Sheet 5' SKI- a. d m

Patented Mar. 23, 1954 1 UNITED STATES VISCOSITY CHANGE COMPENSATION FORHYDRAULIC FEED SYSTEMS Charles Devaud, Geneva,

to Chemical and Mechan Tangier, a corporation of Switzerland, assignorical Processes Limited,

Tangier Application May 23, 1951, Serial No. 228,577

Claims priority,appiic December 2 ation Switzerland 2, 1950 7 Claims.-(01. 6052) The object of the present inventiol'z is a hydraulic powertransmission device. This name is given generally to any assembly ofapparatus for securing the transmission of 'a motion from one place toanother by means of a fluid. Although etymologically the fluid employedshould be Water, the hydraulic power transmission ole-- vices now inoperation use preferably hydrocarbons such as lubricating oils, higheralcohols, fatty alcohols, etc., owing to their lubricating 10 propertiesand their indifference to metals.

The choice of the working liquid depends on different factors such ascompressibility, viscosity, nature of the joints and metals used, etc. FFor the sake of simplicity in this description, we 19 will call thefluid used oil, but it is obvious that any other liquid may be employed.

In a hydraulic power transmission device, the 011 receives energy froman external source such as an electric motor which drives a pump, forinstance, and transmits this energy to any working element, for instancea working piston which moves in a cylinder, a blower, a paddle motor, aturbine etc.

For the sake of clearness in the description, we use throughout theaccount, as working element, the example of the working piston moving ina cylinder. It is understood however that the range of the invention isnot limited to this example, and that the working piston may be Severalfactors intervene in the displacement of the working element and amongthem we will consider here the rate of flow and the pressure of the oil.In the case where the working ing piston in its cylinder according tothe relation:

I in which W=velocity in cm./sec.

=rate of fiow in cm. /s'ec. D='bore of the cylinder in cm.

=pressure in kg/cm? F=force to be overcome in kg. D=bore of the cylinderin cm.

It is obvious that in a hydraulic power transmission, the pressurevaries with the charge on the working piston.

In many applications of hydraulic power transmission the displacemcntvelocity of the working piston must remain as constant as possiblewhatever the load on the latter may he. is mainly the case when suchplant is intended to operate the tools of machine-tools.

In some known plants a volumetric pump with adjustable flow is used forcontrolling the working piston. In fact, the rate of flow in volumetricpumps is theoretically independent of pressure, provided the fluid usedis incompressible. Now, all fluids employed in hydraulic power transtionof the increase of pressure, which may even stop the piston, for a fewmoments should the load on the latter be greatly increased.

If we take into account the error due to the (III) in which W=pistonvelocity Q=rate of flow from the pump at normal pressure R=coefiicientof compressibility of the oil V=oil volume under pressure P=cllpressure.

Therefore the greater the volume of oil used, the greater will be theerror.

In other cases it'ha's been found preferable to use a normal pump, atooth wheel pump for instance, the output of which is in any caseslightly higher than the flow required by the displacement of theworking piston.

The excess oil delivered by the pump is then drawn out of the conduitsbetween the pump and the working piston by means of an overflow valve.

Fig. 1 shows such an arrangement. delivers oil from a tank 2 to aworking piston 4 moving in a cylinder 5. A safety valve 6 limits the oilpressure in the plant. The oil flow to cylinder 5 is regulated by meansof cock 3.

This arrangement is not however adequate to ern'ed by the valve 6.constant. on the other hand, in the piping from Since P2 is variable, Pmay also vary.

If we take into account in relation I as stated above that the flow Q isproportional to the pressure P, we see that the velocity of the workingpiston is influenced by the load on said piston, for a given pumppressure.

The smaller the load on the the higher will be the speed.

Fig. 2 shows a plant in which the working piston 4 is of thedouble-acting type. Furthermore, in this plant, the displacement ofpiston 4 in the direction of its active stroke, i. e. from right to leftin the drawing, is regulated by the outflow through a throttle, cock 3in this case, mounted on a discharge pipe, of a certain regulatingvolume of liquid, proportional to the displacement of working piston 4.

The pressure P2 prevailing in the pipe between cylinder 5 and cook 3 isequal to:

working piston,

where P1 is the pressure determined by valve 6 F is the load on the rodof piston 4 S is the cross-section of the cylinder or the surface ofpiston 4.

It is evident in this case that a variation of the load F causes again avariation of pressure P2 prevailing upstream of cock 3. Pressure P3downstream of cock 3 in the piping between cock 3 and tank 2 is nil. Therate of flow through cock 3 depends therefore on pressure P2.

The hydraulic power transmission device which is the object of thisinvention belongs to that type which includes at least one Workingelement driven by a liquid under pressure, the displacement of thiselement in its active stroke being regularised by the escape through athrottle gap of a certain regulating volume of liquid proportional tothe displacement of the working element.

This hydraulic power transmission device difiers from the known plantsin that upstream of the throttle gap, the regulating liquid works in achamber in which a part at least of the wall may be displaced by thepressure of the regulating liquid. On the other face of the wall acts anopposing force which maintains in position a discharge valve branched onthe inlet pipe conveying the liquid under pressure to the workingelement. It follows that if during a powered stroke of said element, themovement of the latter tends to accelerate, the resulting pressureincrease of the regulating liquid provokes the lifting of the dischargevalve from its seat, thus lessening the pressure of the liquid broughtto the working element and re-establishes automatically the normal speedof travel of the latter,

Figs. 3 to 5 of the annexed drawing show schematically and as examples,three different forms of the invention. 1

In the first form, shown in tained in a tank 2 is driven under pressureby means of pump I into a cylinder 5 in which travel a working piston 4of the double-acting type. At each powered stroke of piston 4, i. e.

Fig. 3, the oil con-v ,tends to accelerate fi0Ws to tank 2 through pipefrom right to left on the drawing, a certain volume of the regulatingliquid is driven out by the face of piston 4 opposite to that on whichacts the liquid under pressure from pump I.

Between the throttle gap, in this particular case cock 3, and cylinder5, pressure P2 of the regulating liquid acts in a chamber 1 in which apart at least of the wall may be displaced by said pressure P2.

It must be pointed out that this pressure P2 tends to reach a valuegiven by relation IV. This chamber 1 is part of a regulating device 8and in the type of model shown, the movable part of the wall isconstituted by a deformable diaphragm 9 which may consist of a sheet ofan elastic plastic substance, natural or synthetic. This diaphragm couldalso be made of metal. Under the effect of the pressure of theregulating liquid, the diaphragm 9 tends to move to left of the diagram,against the action of an opposing force. In this type of model theopposing force is produced by a spring l0 which acts on diaphragm 9through the intermediary of a piston H possessing a mushroom-shapedextremity l2. This regulating device includes a release valve on theinlet pipe leading the liquid under pressure to the working piston 4.The working part of this release valve is formed by part l3 of piston Hwhich is now held against seat l4 by spring H]. A pipe l5 allows theworking liquid to fill an annular space 16 around part it of piston ll.A pipe l8 connects chamber [1 with the tank 2. Pipe 19 leads also totank 2 any leakage of liquid between piston H and its cylinder.

In its resting position and by the action of spring 10, piston I lpresses on seat l4 so that the annular space i6 is closed on all itsfaces and the oil coming from pump I cannot escape in any way. If by theeffect of the pressure exerted on diaphragm 9, the piston II isdisplaced away from its seat l4, a portion of the oil coming from pump lflows through chamber H and pipe 18 towards tank 2. Thus a condition ofpressure stabilization is attained 0n the powered face of piston 4 sothat the pressure exerted on its opposite face will allow the opening ofthe release valve, by moving away part l3 of piston II from its seat 14.An equilibrium is thus established between the thrusts of spring ill andthose of the oil on diaphragm 9. The thrust of the spring beingpractically constant, the oil pressure on the diaphragm and through iton the face of piston 4 upon which acts the regulating liquid, i. e. P2,is also practically constant. The rate of flow through cock 3 will thusbe practically constant, and hence the speed of displacement of piston 4will be likewise constant.

In other words, every time that the piston 4 in its powered stroke, theresulting rise of pressure for the regulating liquid between piston 4and throttle gap 3 provokes the lifting of outlet valve [3 from its seat[4, letting out a certain volume of Working liquid which E5, the annularspace l6, chamber I1 and pipe l8.

This outflow of the working liquid causes therefore a loss of pressureof the liquid delivered to the working piston 4 and re-establishesautomatically the normal speed of travel of the latter.

The regulating device 3, described above, thus works so as to maintainconstant the'pressure P2 prevailing in chamber 1. In fact, it followsfrom the relation IV that if thecondition:

P2=constant cock 3), the rate of flow from cock 3 remains constant andthe speed of displacement of the piston t in cylinder remains likewiseconstant.

Fig. 4 represents diagrammatically a second form of the invention,differing from the first in the fact that the spring it of Fig.3has'been suppressed, and replaced by the action on piston ll of thepressure of the oil supplied by a second pump 20, by means of pipe 2|. Athrottle gap, in the present case a cook 22., allows the pressure of oilon piston ii to be controlled at will. This device has the advantageover the preceding one in allowing a thrust on membrane 9, independentof the position of the piston i l.

Moreover, this device allows an automatic compensation for variations inviscosity of the oil. In fact, the viscosity of the oil varies with itstemperature. Since viscosity plays a part in the speed of how throughthe throttle gap 3, the output is only constant as long as the viscosityremains constant. For example, if as a result of increase in thetemperature of the oil, arising from the working of the pumps, theviscosity diminishes, the output of cock 3 increases for any givenpressure and cross-section of aperture. But in this case, and for thesame reason, the output from valve 22, Whose oil comes from the sametank 2 increases in the same proportion and the counter-pressure exertedon piston H by the oil from pump 28 diminishes. There follows aproportional diminution of the pressure on diaphragm 9, to obtainequilibrium with the counter-pressure acting on piston |i. Hence therefollows a proportional diminution in the output of cock 3, thus ie-establishing the initial conditions.

Fig. 5 represents in outline a third form of the inventionwhose workingis in every way similar to that described with reference to Fig. 4, butwhose regulator device comprises a cylinder 24 enclosing a second-piston23 immovably joined to piston ll. This cylinder 24 is for the purpose ofcorrecting the retarding eifects due to throttling of the oil betweenpiston H and seat M.

Pump 1 feeds on one hand piston 4, and on the other piston 23. Theoutput pressure of pump I, when the discharge valve I3 is closed, isdetermined by two chokes 26 and 21, arranged in series in discharge pipe23. A pipe 25 leading from a point situated between the two chokes 26and 21, each of which consists of a throttle cock, supplies cylinder261. Thus, when the effort on piston 4 increases, the pressure of oil onthe powered surface of the piston 3 should increase; this entails anincrease in pressure in the ring shaped space it. Part l3 of piston l Ishould then, under the influence of diaphragm 9 and the counter-pressureof the oil, move back towards its seat 14, which has the efiect ofaccelerating the speed of the oil between seat I4 and piston II. Thisacceleration tends to push piston ll away from seat it; but piston 23then comes into action, receiving by pipe 25 liquid under a pressureproportional to that acting on the powered surface of the piston i.Piston 23 then tends to move piston ll nearer its seat I4. The value ofthis correction can be controlled by the adjustment of the cocks 26 and21.

In this latter form, the working piston 4 is'ied with working liquid bymeans of a distributor unit 29 which allows the liquid to be sent toeither.

the one or the otherof the two faces of the piston i. In the presentcase this distributor unit 29 is of the slide-valve type 30 which may beoperated automatically by the machine on which the installation ismounted, or by hand. In the position represented by .Fig, 5, the slidevalve 39 allows the working liquid arriving by. supply pipe ill to exertits pressure on surface 32 of piston 4. Hence the latter moves in thedirection of arrow 33 and the liquid pushed back by surface 3 of pistonl escapes through the discharge pipe 35. When the slide valve Si} ispushed towards the left-hand side of Fig. 5, the working liquid acts onthe face 34 of the piston i, and this latter moves in the directionopposite to that shown by the arrow Unit 38 is intended to produceimmobilization of the piston 4. This unit comprises a plug valve 3?inserted in discharge pipe 35. The plug38 of this valve is held on itsseat 3:3 by a spring iii. A cam ll controlled by the machine on whichthe installation is mounted, determines the timing of the opening andThus, each time valve 31' pipe being blocked, the piston t remainsmotionless. The increase in liquid pressure in pipe 25 resulting fromclosure of valve 3? produces movement of piston l3 away from its seat.

i l, and thus the working liquid supplied by pump 2' able to escapetowards tank 2 by pipe it.

In the three forms of hydraulic control device described with referenceto Figs. 3 to 5, the movable part of the wall is 9 could be replaced bya piston whose face would bound chamber face would form a wall ofchamber ll. age of liquid between this piston and its cylinder could becorrected for the condition that the total flow of liquid through thedischarge pipe 35, the flow which determines a minimum and constantspeed of travel of the working piston 4, should not be less than that ofthe said leakage.

As a variation of the above, instead of comprising only a single piston4, with double action, the device could include several pistons;moreover, this or these double-action pistons could be replaced bysingle action pistons whose rod controls the stroke of a single actionpiston working in a cylinder other than cylinder 5. Thus the regulatorliquid itself could be different from the working liquid acting on thepowered surface of piston 4. For this, the installation should includetwo tanks 2, one feeding the pump I, and the other, the pump 20 togetherwith the cylinder receiving the regulator liquid.

The above remark is valid not only for the case where the working agentis a piston, but also for the case where the working agent isconstituted by any working part whatever that can be moved by a movingfluid.

It is to be noticed, moreover, that in all these different models whichare intended especially for application to machine-tools, an appliancecould be designed to produce maximum opening of cock 3 when the piston 4is on its return stroke to its initial position, so that this stroke ismade in minimum time.

closing of this valve 332' is closed, the discharge manometer t2 to pipe2i allows a check to be kept in the output pressure of pump it.

formed by a diaphragm 2. However, it is obvious that this diaphragm.

l on one side, while the opposite A leakby the choice of a given.section of thethrotttle gap 3, subject always to To make the drawingeasier to understand, the units needed to produce the return stroke ofpiston 4 in the models represented by Figs. 3 and 4, have not beenshown. These units can be of the same kind as that shown in Fig. 5, oragain include any arrangements of pipes, valves, cocks, etc., alreadyused in known devices, provided that in this case it is not necessarythat the speed of movement of piston 4 in the negative direction beconstant.

I claim:

1. In a hydraulic power transmission device of the type including atleast one working part to be moved by a liquid under pressure, themovement of this part in the direction of its powered stroke beingregulated by the escape through a throttle gap of a certain volume ofregulator liquid, proportional to the displacement of the working part,wherein, the regulator liquid acts in a chamber of which at least a partof one wall can be displaced by the action of the pressure of theregulator liquid, and against the action of a counter force holding inposition a discharge valve of the inlet pipe bringing liquid underpressure to the working part, so that each time, in the powered strokeof the said working part, its movement tends to accelerate, the increasein pressure in the regulator liquid results in the valve being forcedfrom its seat, which reduces the pressure of the liquid supplied to theworking part, and automatically re-establishes the normal speed ofdisplacement of the latter, and wherein said counter force is producedby a liquid under pressure acting on a piston, to which said dischargevalve is immovably fixed, the improvement which comprises a commonreservoir for the regulator liquid, the liquid acting on said dischargevalve and the liquid actuating said working part, so that any variationin viscosity due to a change or temperature of the liquid produces equalpressure variations on both sides of said displaceable wall and thedischarge valve remains unaffected bytemperature changes of the liquid;two pumps, one of said pumps continuously drawing liquid.

to operate said workof said pumps continuously from said commonreservoir ing part, the second drawing liquid from said common reservoirto produce said counter force; a feed line for the liquid delivered bysaid second pump; and a throttle gap in said feed line to adjust thepressure acting on said discharge valve.

2. Device according to claim 1, the special characteristic of which isthat the discharge valve is immovably fixed to a second piston, on whichacts a liquid under a pressure proportional to that of the liquid whichdrives the working part.

3. Device according to claim 2, the special characteristic of which isthat a common source of liquid under pressure feeds the working part andthe second piston of the discharge valve, two chokes arranged in serieson the discharge pipe of the said source determining the pressure of theliquid supplied thereby, the second piston of the discharge valve beingfed with liquid at a point situated between the two chokes.

4. Device according to claim 3, the special characteristic of which isthat the throttle gaps and the chokes are of adjustable cross-sectionand consist of throttle cocks.

5. Device according to claim 1, the special characteristic of which isthat the surface of the displaceable wall opposite to that on which theregulator liquid acts forms part of the internal wall of the dischargechannel which is controlled by the said valve, so that when this opens,the liquid under pressure which it controls, and which comes from thesource which feeds the working element acts on the said surface.

6. Device according to characteristic of which is consists of adiaphragm.

'7. Device according to characteristic of which is consists of a piston.

claim 1, the special that the movable wall claim 1, the special that themovable wall CHARLES DEVAUD.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,970,181 Monroe Aug. 14, 1934 2,028,766 Ernst et al Jan. 28,1936

